The central control of fetal breathing and movements.

In fetal lambs after 115 days gestation breathing movements become episodic in association with electrocortical differentiation into predominantly high voltage slow or low voltage rapid activity, the latter characteristic of rapid eye movement sleep. Section of the brainstem at or above the colliculi dissociates fetal breathing from electrocortical activity. It is included that breathing is inhibited, towards the end of gestation, by a supracollicular mechanism during high voltage activity. After brainstem transection at the colliculi hypoxia no longer causes an arrest of fetal breathing, which often becomes more vigorous. The arrest of breathing in normal fetuses subjected to mild hypoxia is also attributed to a supracollicular mechanism. The pattern of fetal skeletal movements and of the spinal segmental reflexes is related to electrocortical activity near term; both are suppressed by hypoxia. The hypothesis is discussed of a central control centre, excited directly or indirectly by hypoxia, which inhibits fetal movements including breathing. Its possible location is considered.